Question

我正在使用一个名为＆＃34; LINQ to Access＆＃34;的第三方软件包。我收到以下错误：

System.Data.OleDb.OleDbException about＆＃34;不支持JOIN运算符。＆＃34;

我该如何解决？

 using(var context = AccessTools.CreateDataConnection(connStr)) {
     var tMachine = context.GetTable < Machine > ();
     var tUserinfo = context.GetTable < USERINFO > ();
     var tCheckintoutFiltered = context.GetTable < CHECKINOUT > ().Where(o => o.CHECKTIME >= startTime && o.CHECKTIME <= endTime);

     var join1 = tCheckintoutFiltered.Join(
       tMachine,
       outer => outer.sn,
       inner => inner.sn, (outer, inner) => new {
         outer.USERID, outer.CHECKTIME, outer.CHECKTYPE, inner.MachineNumber
       });

     var join2 = join1.Join(
       tUserinfo,
       outer => outer.USERID,
       inner => inner.USERID, (outer, inner) => new AttendanceLogObject {
         Checktime = outer.CHECKTIME, Checktype = outer.CHECKTYPE, MachineNumebr = outer.MachineNumber, Badgenumber = inner.Badgenumber
       });


     foreach(var alo in join2) {
       list.Add(new AttendanceLogObject { Checktime = alo.Checktime., Checktype = alo.Checktype, MachineNumebr = alo.MachineNumebr, Badgenumber = alo.Badgenumber });
     }

}

Answer 1

如果包不支持特定功能，那么“解决”它的唯一方法是：

说服软件包的开发人员实现该功能，或
如果它是一个开源项目，那么请下载该软件包的源代码并自行实现该功能。

否则，您需要使用产品支持的功能“解决”问题。例如表[参与者] ......

ID  FirstName  MedalID  Event
--  ---------  -------  -----------
 1  Gord             1  Napping
 2  Helen            3  Daydreaming

......和[奖牌] ......

ID  Name
--  ------
 1  Gold
 2  Silver
 3  Bronze

......我真的希望能够做到这一点：

var particips = from p in db.Participants 
                join m in db.Medals on p.MedalID equals m.ID 
                select new { p.FirstName, MedalName = m.Name, p.Event };
foreach (var particip in particips)
{
    Console.WriteLine(
            "{0} won a {1} medal in \"{2}\"", 
            particip.FirstName, 
            particip.MedalName, 
            particip.Event);
}

但如果不支持join，我可能不得不这样做：

var medalNames = new Dictionary<int, string>();
var medals = from m in db.Medals select m;
foreach (var medal in medals)
{
    medalNames.Add(medal.ID, medal.Name);
}
var particips = from p in db.Participants 
                where p.MedalID != null
                select p;
foreach (var particip in particips)
{
    Console.WriteLine(
            "{0} won a {1} medal in \"{2}\"", 
            particip.FirstName, 
            medalNames[(int)particip.MedalID],
            particip.Event);
}

LINQ to Access不支持JOIN

1 个答案: